An aircraft is driven by a plurality of turbojet engines, each accommodated in a nacelle likewise housing an assembly of accessory actuating devices associated with its functioning and ensuring various functions when the turbojet engine is in operation or at a standstill. These accessory actuating devices comprise, in particular, a mechanical system for the actuation of thrust reversers.
A nacelle generally has a tubular structure comprising an air inlet in front of the turbojet engine, a middle section intended for surrounding a blower of the turbojet engine, and a rear section capable of housing thrust reversal means and intended for surrounding the combustion chamber of the turbojet engine, and generally terminates in an ejection nozzle, the outlet of which is located downstream of the turbojet engine.
Modern nacelles are often intended for housing a double-flow turbojet engine capable of generating, by means of the rotating blades of the blower, a stream of hot air (also called a primary stream) coming from the combustion chamber of the turbojet engine.
A nacelle generally has an external structure, called an outer fixed structure (OFS), which, with a concentric internal structure, called an inner fixed structure (IFS), defines an annular flow channel, also called a flow section, intended for channeling a stream of cold air, called a secondary stream, which circulates outside the turbojet engine. The primary and secondary streams are ejected from the turbojet engine at the rear of the nacelle.
Each propulsive assembly of the aircraft is thus formed by a nacelle and a turbojet engine and is suspended from a fixed structure of the aircraft, for example under a wing or on the fuselage, by means of a pylon or mast attached to the turbojet engine or to the nacelle.
The rear section of the external structure of the nacelle is usually formed from a first and a second half-shell of substantially semi-cylindrical shape, on either side of a vertical longitudinal plane of symmetry of the nacelle, and mounted movably so as to be capable of being deployed between an operating position and a maintenance position for the purpose of giving access to the turbojet engine. The two half-shells are generally mounted pivotably about a longitudinal axis forming a hinge in the upper part (at 12 o'clock) of the reverser. The half-shells are held in a closing position by means of locking devices arranged along a junction line located in the lower part (at 6 o'clock).
Conventionally, the two half-shells are, in particular, connected to one another in the region of a front frame, which makes it possible to attach the rear section to a fixed part of the middle section, by means of at least one locking device comprising a locking member equipping the first half-shell, a complementary locking member equipping the second half-shell, and a control handle fastened in the first half-shell and connected to the locking member by transmission means.
The control handle is usually designed so as to be capable of being displaced alternately from a stable opening position, in which the locking member is open, to a stable locking position, in which the locking member is closed, passing through an unstable intermediate phase where the locking member is closed.
This control handle is equipped with a secondary locking system comprising a blocking member making it possible, once placed in the blocking position, to block said control handle in its locking position. For this purpose, the control handle comprises a trigger which has to be actuated beforehand by the operator in order to make it possible to rotate said control handle in the direction of its locking position. Once the latter is reached, the operator can release the trigger, thus causing the translational motion of the blocking member in the control handle and its engagement in an orifice located in an internal piece, for the purpose of blocking the control handle in its locking position.
The middle section is conventionally formed from at least two shrouds mounted movably in rotation about a longitudinal axis so as each to be capable of being deployed between an operating position and a maintenance position. These shrouds are designed, in particular, so that their rear ends come into position around the front frame when they are in the operating position, and therefore cover the control handle of the locking device.
In the opening position, the control handle projects from the junction line located in the lower part and is generally visible from outside.
In the intermediate position, or when the blocking member is not in its blocking position, that is to say when the trigger is not engaged, a slight lack of attention on the operator's part is sufficient for him to fail to detect that the control handle is not in its locking position. Experience has shown that shrouds have been turned down and locked in the operating position when the control handle has been in the intermediate position or the blocking member has not been in its blocking position. Such a situation is especially disturbing because, since the control handle is unstable in this position, the locking member may come to be disengaged from the complementary locking member under the effect of external stresses.